In the formation of a ruthenium thin film or a ruthenium compound thin film by a chemical vapor deposition method such as chemical vapor deposition (CVD) or atomic layer vapor deposition (ALD), as raw material compounds therefor, a large number of organic ruthenium compounds is known. Among such organic ruthenium compounds, in recent years, dodecacarbonyl triruthenium represented by following formula (hereinafter referred to as DCR) is hoped to be put to practical use.

DCR is a substance having a melting point of 154 to 155° C., which is solid (orange crystalline) at normal temperature. DCR has a simple molecular structure composed only of Ru and CO, and film can be formed only by thermal decomposition, without use of a reactant gas. Further, in the formed thin film, impurities, such as hydrocarbon, are less likely to remain. Additionally, even though DCR is a solid material, the thin film production efficiency is not adversely affected when the material container is regulated, or the process is suitably controlled. Therefore, its utilization is expected.
Examples of a known production method for such DCR include a method in which a ruthenium compound is carbonylated to synthesize DCR, and then the synthesized DCR is purified (Patent Document 1). When such DCR after synthesis is used for the formation of a ruthenium thin film in an unpurified state, ignition may occur upon the opening of the material container for thin film formation. As a cause of such ignition, the presence of impurity elements such as Fe, Al, and Cr in DCR after synthesis, which are derived from and incorporated from the raw material or the constituent materials of the equipment, can be mentioned. Therefore, DCR after synthesis is preferably subjected to a purification step, such as a sublimation method.
DCR has the property of easily sublimating at a reduced pressure, and thus is suitable for purification by a sublimation method. Specifically, when DCR having a high sublimation pressure is preferentially sublimated and recovered, impurity elements having a low sublimation pressure, such as Fe, can be separated from DCR. The operation process of a sublimation method is relatively simple. Therefore, the loss of the desired material is low, and the purity of DCR can be efficiently improved.